Maximum Jumping Research Articles

Rupture Propagation along Stepovers of Strike-Slip Faults: Effects of Initial Stress and Fault Geometry

ABSTRACTLarge earthquakes on strike-slip faults often rupture multiple fault segments by jumping over stepovers. Previous studies, based on field observations or numerical modeling with a homogeneous initial stress field, have suggested that stepovers more than ∼5 km wide would stop the propagation of rupture, but many exceptions have been observed in recent years. Here, we integrate a dynamic rupture model with a long-term fault stress model to explore the effects of background stress perturbation on rupture propagation across stepovers along strike-slip faults. Our long-term fault models simulate steady-state stress perturbation around stepovers. Considering such stress perturbation in dynamic rupture models leads to prediction of larger distance a dynamic rupture can jump over stepovers: over 15 km for a releasing stepover or 7 km for a restraining stepover, comparing with the 5 km limit in models with the same fault geometry and frictional property but assuming a homogeneous initial stress. The effect of steady-state stress perturbations is stronger in an overlapping stepover than in an underlapping stepover. The maximum jumping distance can reach 20 km in an overlapping releasing stepover with low-static frictional coefficients. These results are useful for estimating the maximum length of potential fault ruptures and assessing seismic hazard.

Study of coalescence-induced droplet jumping during phase-change process in the presence of noncondensable gas

The coalescence-induced condensation droplet jumping on subcooled surface is simulated using the pseudo-potential lattice Boltzmann method, especially the coupled phase-change condensation process and the large amount of noncondensable gas are taken into account. The method is validated by the density distribution of two components inside and outside droplet, the contact angle of droplet spreading on wettability surface as well as the condensing droplet diameter under various noncondensable gas fractions. The effects of noncondensable gas fraction, wettability as well as subcooled surface temperature on condensation heat transfer during droplet nucleation, growth and departure are investigated. The results indicate that the increase of noncondensable gas fraction causes higher resistance to condensable gas diffusion, leading to a reduction of local heat flux near the triple-phase contact line area. Correspondingly, both the coalesced droplet diameter and its maximum jumping height decrease with the increase of noncondensable gas fraction. Compared to the hydrophobic surface, the hydrophilic surface is more favorable for attracting condensable gas and results in a faster onset of nucleation and a higher droplet condensing rate. Moreover, a higher surface subcooling degree accelerates droplet growth and promotes droplet jumping to a higher height. The energy conversion of the removal droplet is also examined. The present work not only demonstrates the capacity of the lattice Boltzmann method but also sheds light on the mechanism of coalescence-induced condensation droplet jumping in the presence of noncondensable gas.

Sensitivity of the novel two-point force-velocity model: an assessment of leg muscle mechanical capacities

ABSTRACT The recently proposed two-point force-velocity (F-V) model requires further evaluation in order to develop into a simple tool for muscle mechanical capacities assessment. Therefore, the first aim of this study was to assess the concurrent validity of the proposed model. The second aim of this study was to assess the sensitivity of the proposed model concerning participants of different levels of physical fitness when performing different dynamic tasks. Female elite volleyball players (N = 10; age 22 ± 2 years) and female physical education students (N = 10; age 22 ± 2 years) were tested on maximum countermovement jumps (CMJ) and 6 s maximal cycling sprint (MCS), where manipulation of loads provided a range of F and V data. The assessed F-V relationships were valid in comparison with the standard model. Moreover, the concurrent validity of the maximum force parameter (F0) was high for MCS (r ≥ 0.89) and moderate to low for CMJ (r = 0.43). Sensitivity analysis revealed significant differences between F0 in both leg tests (p < 0.04), along with maximum power parameter in CMJ (p = 0.034) between the groups. The proposed model could provide sport practitioners with a straightforward and very effective tool for assessing muscle mechanical capacities.

Dynamic and energy analysis of coalescence-induced self-propelled jumping of binary unequal-sized droplets

The coalescence-induced self-propelled droplet jumping on superhydrophobic surfaces has a large number of potential applications such as enhancement of condensation heat transfer, self-cleaning, and anti-icing, which becomes a current hotspot. At present, most of the research studies focus on the self-propelled jumping of two identical droplets; however, the jumping induced by unequal-sized droplets is much closer to actuality. In this paper, the coalescence-induced self-propelled jumping of binary unequal-sized droplets is simulated and all energy terms are studied. The normalized liquid bridge width induced by unequal-sized droplets is a function of the square root of the normalized time, and the maximum jumping velocity is a function of the radius ratio as well. The maximum jumping velocity descends with the decrease in the radius ratio and contact angle, and the critical radius ratio shows an upward trend with the decrease in the contact angle. Furthermore, all energy terms decline with the decrease in the radius ratio. The effective energy conversion rate of binary equal-sized jumping is very low, less than 3% in our results. This rate of binary unequal-sized jumping further reduces due to the existence of asymmetric flow. This work helps for a better understanding of the characteristics of coalescence-induced self-propelled droplet jumping.

Critical and Optimal Wall Conditions for Coalescence-Induced Droplet Jumping on Textured Superhydrophobic Surfaces.

The effectiveness of coalescence-induced jumping of microdroplets on superhydrophobic surfaces is critical to a wide range of applications such as self-cleaning surfaces, anti-icing/frosting, water harvesting, phase-change heat transfer, and hotspot cooling. Introducing textures on the surfaces can readily enlarge the effective contact angle, while an overlarge texture spacing may unfavorably lead to droplet penetration into the gaps in droplet coalescence processes. To clarify the effect of surface textures on the droplet jumping dynamics, we simulated the coalescence of droplets on textured superhydrophobic surfaces with various surface wettability and texture spacings and theoretically derived the critical conditions of jumping and the optimal condition of maximum jumping velocity. The results show that the nonmonotonic emergence of "nonjumping"-"jumping"-"nonjumping" with decreasing solid fraction is synergistically controlled by the surface adhesion and the effective impinging pressure. At a large solid fraction, the transition from "nonjumping" to "jumping" is caused by the reduction of the dimensionless surface adhesion energy below a critical value, which is determined to be 0.035 for Oh = 0.02 and 0.01 for Oh = 0.12. At a small solid fraction, the transition from "jumping" to "nonjumping" is dominated by the reduction of the dimensionless effective impinging pressure, the critical value of which is identified to be 0.14 and is independent of Oh. Moreover, jumping velocity maximizes when wetting critically transits from the Cassie-Baxter (CB) state to the partial-wetting state, and a penetration index is proposed from the wetting theory to predict such transition, which shows good agreement with both present simulations and previous experiments. The present findings are helpful for the design of superhydrophobic surfaces that pursue robust and efficient jumping of droplets.

Dynamic Rupture Modeling to Investigate the Role of Fault Geometry in Jumping Rupture Between Parallel‐Trace Thrust Faults

AbstractInvestigations of historic surface‐rupturing thrust earthquakes suggest that rupture can jump from one fault to another up to 8 km away. Additionally, there are observations of jumping rupture between thrust faults ∼50 km apart. In contrast, previous modeling studies of thrust faults find a maximum jumping rupture distance of merely 0.2 km. Here, we present a dynamic rupture modeling parameter study that attempts to reconcile these differences and determines geometric and stress conditions that promote jumping rupture. We use the 3D finite‐element method to model rupture on pairs of thrust faults with parallel surface traces and opposite dip orientations. We vary stress drop and fault strength ratio to determine conditions that produce jumping rupture at different dip angles and different minimum distance between faults. We find that geometry plays an essential role in determining whether or not rupture will jump to a neighboring thrust fault. Rupture is more likely to jump between faults dipping toward one another at steeper angles, and the behavior tapers down to no rupture jump in shallow dip cases. Our variations of stress parameters emphasize these toward‐orientation results. Rupture jump in faults dipping away from one another is complicated by variations of stress conditions, but the most prominent consistency is that for mid‐dip angle faults rupture rarely jumps. If initial stress conditions are such that they are already close to failure, the possibility of a long‐distance jump increases. Our models call attention to specific geometric and stress conditions where the dynamic rupture front is the most important to potential for jumping rupture. However, our models also highlight the importance of near‐field stress changes due to slip. According to our modeling, the potential for rupture to jump is strongly dependent on both dip angle and orientation of faults.

Why do Large Animals Never Actuate Their Jumps with Latch-Mediated Springs? Because They can Jump Higher Without Them.

As animals get smaller, their ability to generate usable work from muscle contraction is decreased by the muscle’s force–velocity properties, thereby reducing their effective jump height. Very small animals use a spring-actuated system, which prevents velocity effects from reducing available energy. Since force–velocity properties reduce the usable work in even larger animals, why don’t larger animals use spring-actuated jumping systems as well? We will show that muscle length–tension properties limit spring-actuated systems to generating a maximum one-third of the possible work that a muscle could produce—greatly restricting the jumping height of spring-actuated jumpers. Thus a spring-actuated jumping animal has a jumping height that is one-third of the maximum possible jump height achievable were 100% of the possible muscle work available. Larger animals, which could theoretically use all of the available muscle energy, have a maximum jumping height that asymptotically approaches a value that is about three times higher than that of spring-actuated jumpers. Furthermore, a size related “crossover point” is evident for these two jumping mechanisms: animals smaller than this point can jump higher with a spring-actuated mechanism, while animals larger than this point can jump higher with a muscle-actuated mechanism. We demonstrate how this limit on energy storage is a consequence of the interaction between length–tension properties of muscles and spring stiffness. We indicate where this crossover point occurs based on modeling and then use jumping data from the literature to validate that larger jumping animals generate greater jump heights with muscle-actuated systems than spring-actuated systems.

Numerical Simulation of Jumping Droplet Condensation.

Jumping droplet condensation has been shown to enhance heat transfer performance (≈100%) when compared to dropwise condensation by reducing the time-averaged droplet size (≈10 μm) on the condensing surface. Here, we develop a rigorous, three-dimensional numerical simulation of jumping droplet condensation to compute the steady-state time-averaged droplet size distribution. To characterize the criteria for achieving steady state, we use maximum radii (Rmax) tracking on the surface, showing that Rmax settles to an average in time once steady state is reached. The effects of the minimum jumping radius (0.1-10 μm), maximum jumping radius, apparent advancing contact angle (150-175°), and droplet growth rate were investigated. We provide a numerical fit for the droplet size distribution with an overall correlation coefficient greater than 0.995. The heat transfer performance was evaluated as a function of apparent contact angle and hydrophobic coating thickness, showing excellent agreement with prior experimentally measured values. Our simulations uncovered that droplet size mismatch during coalescence has the potential to impede the achievement of steady state and describe a new flooding mechanism for jumping droplet condensation. Our work not only develops a unified numerical model for jumping droplet condensation that is extendable to a plethora of other conditions but also demonstrates design criteria for nonwetting surface manufacture for enhanced jumping droplet condensation heat transfer.

Is There a Trade-Off Between Maximum Jumping and Throwing Capability in the Handball Jump Throw?

This study examined the potential trade-off in performance between maximum physical capabilities in the handball jump throw, a fundamental skill comprised of two mechanically independent tasks. Elite handball players performed jump throw actions from a force plate for each of three instructions: jump at maximum capability, throw at maximum capability, and jump and throw at maximum capability simultaneously. Jump height and throwing velocity were derived from motion capture data. When jumping and throwing at maximum capability simultaneously, no trade-off between jump height and throwing velocity was present, but rather a concurrent decline from their respective maximums. This decline could be explained by mechanical factors related to movement execution; magnitudes of directional impulses favored vertical movement for jumping and horizontal movement for throwing. However, no explanation for differences in total magnitude of impulse between instructions was evident. Due to the expertise of the participants, information processing should not be a limiting factor, leaving movement strategy as the most likely explanation for the present findings.

Acute Effects of Neuromuscular Electrical Stimulation on Vertical Jump

Yusuf K. Kaire, Andrew Harveson, Dominick Sturz, Levi Garrett California Baptist University, CA Multiple studies have indicated improvements in muscular strength, power, and performance can be made over time using neuromuscular electrical stimulation (NMES). Yet no previous studies have conducted research into the effects of NMES on vertical jump immediately after isometric stimulation to the quadriceps group. PURPOSE: To determine the acute effects of NMES on vertical jump. METHODS: A group of 24 participants were randomly divided into an experimental and a control group. All participants were pretested in the countermovement jump (CMJ) to determine maximum jumping height. Participants in the treatment group were treated with NMES to the quadriceps. Participants in the control group received sham treatment in identical testing conditions. All participants then engaged in a post treatment CMJ test. The difference between pretest and posttest jump scores was computed to determine the effects of treatment. RESULTS: A paired samples t-test showed a statistically significant increase in experimental CMJ scores from pre-test (M = 28.69, SD = 6.87) to posttest (M = 30.14, SD = 7.42), t(11) = 1.796, p <. 05. (Figure 1). A statistically significant decrease in control CMJ scores occurred from pre-test (M = 30.72, SD = 6.51) to posttest (M = 29.18, SD = 6.24), t(11) = 1.796, p <. 05. The mean increase in experimental CMJ scores was 1.45 with a 95% confidence interval ranging from 26.61 to 33.67. The mean decrease in control CMJ scores was 1.54 with a 95% confidence interval ranging from 26.21 to 32.15. Cohen’s d (.24) indicated a small effect size. CONCLUSION: The acute application of NMES to the quadriceps group lead to significant improvements in vertical performance.

Jumping dynamics of aquatic animals.

Jumping out of water is a phenomenon exhibited by a variety of aquatic and semi-aquatic animals. Yet, there is no common groundwork that clarifies the physical constraints required to jump out of water. In this study, we elucidate the physical conditions required for an animal to jump out of water. More than 100 jumps are analysed over five taxonomic groups. By balancing the power produced by animals with drag-induced dissipation, we expect that maximum jumping height, H, scales with body length, L, as H/ L ∼ L-1/3 ∼ Fr2, where the Froude number, Fr, is a ratio of inertia to gravity. To identify jumping regimes, simplified experiments are conducted by shooting axisymmetric bodies through the water surface. Here, we see a transition in which partial exits scale as H/ L ∼ Fr and complete exits scale as H/ L ∼ Fr2. A bioinspired robotic flapping mechanism was designed to mimic the fast motion of impulsive jumping animals. When exiting water, the robot carries a large volume of fluid referred to as an entrained mass. A theoretical model is developed to predict the jumping height of various water-exiting bodies, which shows that the mass of the entrained fluid relative to the mass of the body limits the maximum jumping height. We conclude that the lack of entrained fluid allows animals to reach extraordinary heights compared to our water-exiting robots.

Effects of Reduced Effort on Mechanical Output Obtained From Maximum Vertical Jumps.

The aim of this study was to evaluate the effect of reduced effort on maximum countermovement jumps. Groups of unskilled and skilled jumpers performed countermovement jumps without an arm swing at 100% and 50% effort. The results revealed markedly reduced jump height and work performed at 50% effort, although the maximum force and power output remained virtually unchanged. The observed differences were consistent across individuals with different jumping skills. A possible cause of differences in changes across the tested variables was a reduced countermovement depth associated with the 50% effort jumps. It is known to cause an increase in maximum force and power outputs, but not in jump height. Therefore, the jump height and work performed may be more closely related to our sense of effort when jumping, rather than our maximum force and power output. From a practical perspective, the present findings reiterate the importance of maximizing effort for making valid assessments of muscle mechanical capacities, as tested by maximal vertical jumps and, possibly, other maximum performance tasks.

Reliability of independent kinetic variables and measures of inter-limb asymmetry associated with bilateral drop-landing performance

The purpose of this investigation was to establish the within-session reliability for peak vertical ground reaction force (vGRF), time to peak vGRF, and loading rate, both unilaterally and bilaterally, during a drop-landing task as well as the reliability of inter-limb asymmetry in peak vGRF. Twenty-two men (age = 22 ± 4 years; height = 180.4 ± 6.1 cm; mass = 77.9 ± 14.0 kg) and 17 women (age = 20.4 ± 3.6 years; height = 164.6 ± 9.4 cm; mass = 60.3 ± 9.8 kg) volunteered for a single testing session. Participants completed three maximum countermovement jumps (CMJ) to establish maximum jump height before performing five bilateral drop-landings from 50%, 100%, and 150% of their maximum CMJ height. The bilateral drop-landing protocol was then repeated after a 10 min recovery. Systematic bias, intraclass correlation coefficient (ICC), coefficient of variation (CV%) and minimal detectable change (MDC) values for each kinetic measurement was calculated for the left and right leg, as well as their average. There was no systematic bias present between trials (P &gt; 0.05). All kinetic measurements showed relative reliability, ranging from large to near perfect (ICC = 0.57–0.95). Absolute reliability ranged considerably depending on the measure and drop-height, with peak vGRF and time to peak GRF showing the greatest reliability at higher drop heights (CV% = 6.6–9.7%). Loading rate for all drop heights demonstrated CV% ranging 13.0–27.6%. Furthermore, MDC values for inter-limb asymmetries in peak vGRF ranged between 14.5–16.2% for all drop heights. Overall, many of the kinetic measurements evaluated were sufficiently reliable to detect typical changes in bilateral drop-landing performance when greater drop heights were used.

Electrostatic-induced coalescing-jumping droplets on nanostructured superhydrophobic surfaces

Coalescing-jumping droplets from the condensation of water vapor on a non-wetting surface return to the substrate due to resistance forces. While some can coalesce with neighboring droplets and jump again, some adhere to the surface and become larger, leading to progressive flooding, limiting heat transfer performance. To address these issues, an electric field is utilized. This study investigates the jumping height, the droplet charge, the jumping angle, the gravitational force, the drag force, the inertia force and the electrostatic force of coalescing-jumping droplets in electric fields through experiment and mathematical models. The results show that an electric field can enhance the jumping height due to a significant increase in the electrostatic force. With the applied electric field, the maximum jumping height is over three times higher than those without. Additionally, the study reports the intersection point at the jumping droplet radius of 35 μm separating jumping droplet motion into two regimes; the drag-force-dominated regime where the small-sized droplets can jump and reach the top plate, and the gravitational-force-dominated regime where the larger droplets can jump, but return to the substrate. The other intersection point is between the gravitational force and the inertia force showing a decrease in the influence of the inertia force with a greater applied electric field. Moreover, it is also found that the average charge of the droplets is relatively constant in all pressure conditions and applied electric fields. The results of these findings can further advance knowledge on the enhancement of heat transfer and can be applied to several applications including self-cleaning, smart windows, thermal diodes and condensation heat transfer enhancement.

Effect of radius ratios of two droplets on coalescence-induced self-propelled jumping

The coalescence-induced self-propelled droplet jumping behaviors on superhydrophobic surfaces have attracted extensive interest, due to a huge application potential. The coalescence and jumping of two droplets with different radius ratios are numerically simulated, and the jumping velocity is theoretically analyzed. The jumping type changes from the vertical motion to the upward rotation motion, with the decrease of radius ratio. The droplet is not able to jump when the radius ratio is smaller than 0.4. The jumping velocity reaches several peak values when the radius ratio is smaller than 0.7. The maximum jumping velocities are theoretically predicted, which is based on the law of conservation of energy. The viscous dissipation energy which should not be ignored is the main and direct source of the errors.

The influence of weather-climatic and social factors on population mortality from circulatory diseases in Russia.

To study the links between the standard mortality rate of the population from circulatory system diseases (CSD) with factors: weather-climatic (inter-day jumps in air temperature and atmospheric pressure by seasons and for the year) and social (average annual income per person and the number of doctors of all specialties) in Russia for the period 1995-2015. According to station data and data of reanalysis, seasonal and annual amounts of day-to-day jumps in air temperature were calculated more than the absolute value of 4° and 6°C and the atmospheric pressure more than the absolute value of 8 GPa. The links between climate variables and the mortality rate of the population, taking into account social factors, were investigated using factor analysis, including regression and variance analyses. Annual amounts of temperature (pressure) jumps of different signs vary greatly on the territory: the maximum amounts are 3-4 times higher than the minimum ones. The geographical distribution of air temperature fluctuations differs from the distribution of atmospheric pressure fluctuations. The sum of temperature jumps in the absolute value of more than 6°C is about twice less than the sum of jumps more than 4°C, but they are characterized by similarity of geographical distribution. The sum of the jumps of temperature (pressure) is reduced during the summer is approximately two times compared to the winter. The maximum jumps are observed mainly in the Northern regions with low population density, but with high per capita income, while the minimum is observed in the South-Western parts of the European part of the country with high population density, as well as middle and low income. Global warming does not significantly affect the reduction of annual amounts of temperature (pressure) jumps. Factor analysis of social and climatic variables in the territory for each year indicates the dominance of the influence of the social factor (per capita income) on the mortality rate from CSD. Factor analysis is integrated in the annual scale climatic and social variables showed a dominant effect on the coefficient of mortality from CSD, the factor of standard of living (per capita income of the population). Then the significance of the impact factors is consistently reduced: negative atmospheric pressure jumps, average seasonal pressure, health care level, positive pressure jumps. The significance of temperature variables is the smallest.

Relationships Between Countermovement Jump Ground Reaction Forces and Jump Height, Reactive Strength Index, and Jump Time.

Barker, LA, Harry, JR, and Mercer, JA. Relationships between countermovement jump ground reaction forces and jump height, reactive strength index, and jump time. J Strength Cond Res 32(1): 248-254, 2018-The purpose of this study was to determine the relationship between ground reaction force (GRF) variables to jump height, jump time, and the reactive strength index (RSI). Twenty-six, Division-I, male, soccer players performed 3 maximum effort countermovement jumps (CMJs) on a dual-force platform system that measured 3-dimensional kinetic data. The trial producing peak jump height was used for analysis. Vertical GRF (Fz) variables were divided into unloading, eccentric, amortization, and concentric phases and correlated with jump height, RSI (RSI = jump height/jump time), and jump time (from start to takeoff). Significant correlations were observed between jump height and RSI, concentric kinetic energy, peak power, concentric work, and concentric displacement. Significant correlations were observed between RSI and jump time, peak power, unload Fz, eccentric work, eccentric rate of force development (RFD), amortization Fz, amortization time, second Fz peak, average concentric Fz, and concentric displacement. Significant correlations were observed between jump time and unload Fz, eccentric work, eccentric RFD, amortization Fz, amortization time, average concentric Fz, and concentric work. In conclusion, jump height correlated with variables derived from the concentric phase only (work, power, and displacement), whereas Fz variables from the unloading, eccentric, amortization, and concentric phases correlated highly with RSI and jump time. These observations demonstrate the importance of countermovement Fz characteristics for time-sensitive CMJ performance measures. Researchers and practitioners should include RSI and jump time with jump height to improve their assessment of jump performance.

Assessing the Relationship Between Vertical Jump Performance and FMS in Young Adult Males

Functional Movement Screening (FMS) is an assessment test used to determine an athlete’s risk of injury based on the scores of seven tests that utilize commonly used movement patterns during exercise. Each test is scored based on whether or not biomechanical deficiencies are present when performing each test. Prior research has predominantly evaluated the relationship between FMS and susceptibility to injury. Yet, there appears to be limited research with FMS and anaerobic performance. Specifically, the relationship between FMS and vertical jump performance has not yet been addressed. PURPOSE: To determine the correlation between Functional Movement Screening scores and maximum vertical jump height in young adult males. METHODS: Thirty averagely fit males (Age = 23.13 + 3.02 yrs, HT = 178.74 + 8.00 cm, WT = 82.14 + 13.46 kg, BF% = 14.32 + 4.60) voluntarily participated in this study. Each subject performed FMS and were scored according to the grading criteria provided by the developers of FMS. Then a dynamic warm-up utilizing a cycle ergometer for 8 min was performed followed by a 4 min passive recovery period. Next, subjects performed four maximum effort vertical jumps, which served as their vertical jump familiarization trials. All jumps were separated by 30 seconds except the last jump of the familiarization trial and the first jump of the performance trials which were separated by 4 min of passive recovery. The highest of the four performance jump trials, excluding the first jump, was utilized for data analysis. Pearson Correlations were utilized to assess the relationship maximum vertical jump height and total FMS score, squat FMS score, and inline lunge FMS score. RESULTS: There was a slight positive correlation when comparing maximum vertical jump (69.51 + 9.68 cm) to total FMS score (r = .264) and FMS squat score (r = .170), but there was a moderate positive relationship with FMS inline lunge score (r = .421), which was significantly higher (p = .01) than both FMS total and FMS squat scores. CONCLUSION: The results of the current study seem to suggest that total FMS score is not a significant predictor for maximum vertical jump height. However, future studies should seek to determine the potential impact that improvements in the FMS inline lunge, squat, and total score may have on vertical jump performance.

Does trampoline or hard surface jumping influence lower extremity alignment?

[Purpose] To determine whether repetitive trampoline or hard surface jumping affects lower extremity alignment on jump landing. [Subjects and Methods] Twenty healthy females participated in this study. All subjects performed a drop vertical jump before and after repeated maximum effort trampoline or hard surface jumping. A three-dimensional motion analysis system and two force plates were used to record lower extremity angles, moments, and vertical ground reaction force during drop vertical jumps. [Results] Knee extensor moment after trampoline jumping was greater than that after hard surface jumping. There were no significant differences between trials in vertical ground reaction force and lower extremity joint angles following each form of exercise. Repeated jumping on a trampoline increased peak vertical ground reaction force, hip extensor, knee extensor moments, and hip adduction angle, while decreasing hip flexion angle during drop vertical jumps. In contrast, repeated jumping on a hard surface increased peak vertical ground reaction force, ankle dorsiflexion angle, and hip extensor moment during drop vertical jumps. [Conclusion] Repeated jumping on the trampoline compared to jumping on a hard surface has different effects on lower limb kinetics and kinematics. Knowledge of these effects may be useful in designing exercise programs for different clinical presentations.

Water striders adjust leg movement speed to optimize takeoff velocity for their morphology

Water striders are water-walking insects that can jump upwards from the water surface. Quick jumps allow striders to avoid sudden dangers such as predators' attacks, and therefore their jumping is expected to be shaped by natural selection for optimal performance. Related species with different morphological constraints could require different jumping mechanics to successfully avoid predation. Here we show that jumping striders tune their leg rotation speed to reach the maximum jumping speed that water surface allows. We find that the leg stroke speeds of water strider species with different leg morphologies correspond to mathematically calculated morphology-specific optima that maximize vertical takeoff velocity by fully exploiting the capillary force of water. These results improve the understanding of correlated evolution between morphology and leg movements in small jumping insects, and provide a theoretical basis to develop biomimetic technology in semi-aquatic environments.